[Ipopt] Very slow convergence

[Nicolas Gachadoit]

Hello,

I use Ipopt for Optimal Control (minimum time control) and in one of my 
applications, the convergence is very slow.
It is a robotic application (4 dof), the equations (constraints and 
gradient of constraints, automatically generated by Maple) are very big 
so it could be the reason but on another hand, in another application (5 
dof), the convergence is fast (< 2000 iterations, less than 2 minutes).
In this application (4 dof), I tried up to 20000 iterations and it did 
not converge yet. Each time I increase max_iter, it is better (the 
minimum time decreases and the controls are closer to saturations) so a 
possibility would be to try to put a very high max_iter and wait for a 
few hours.
But I would like to know if another option could make the convergence 
faster. Maybe it is a problem of scaling or something else ?

Thanks in advance,
Best regards,

Nicolas Gachadoit
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